Although The Flash's intro announces Barry Allen as the fastest man alive, is he really?

Now that Zoom is in the picture, the villain would argue that he, Jay Garrick, aka Hunter Zolomon, is actually the fastest speedster in the multiverse. In the season finale, Zoom challenges Barry to one last race that will not only determine who gets to hold that title, but also affects the fate of all worlds.

Things are already looking down for Barry: in a shocking twist during last week's episode, Zoom killed his father. Now, Barry has revenge on his mind, although his friends warn him that if he goes after the bad guy only seeking that, he will lose.

In a new promo for the final episode of the season, Zoom challenges Barry, who still struggles with the loss of his father. The preview also teases that Zoom plans on destroying multiple Earths and only Barry can stop him. That means it's now just Flash vs. Zoom, with the winner taking all.

So, will the death of Barry's father affect the Flash's final battle with Zoom? Actor Grant Gustin, who portrays the character, promises that, although things are bad for Barry now, he'll pull through with the same optimism that fans expect from him.

"We've seen him in darkest places, but the thing about Barry Allen, the Flash, he's an optimistic character, and his kind of way of life is to keep moving forward and to stay as positive as possible," Gustin said to TV Line. "I think it would be harder for him going into season three, but I think we'll still see Barry fighting for his optimism and trying to move on with his life."

It helps that Barry is no stranger to grief, having lost his mother at a young age. This will also help him deal with his father's death.

"He lost his mom at a young age, he saw her right in front of him, then went back in time and watched it again ... he'll find a way to deal with this," Gustin said to ComicBook.com. "He's not going to let it ruin him. It's going to be hard to come back from this one, but he'll stay optimistic Barry."

The Flash season finale airs on The CW on May 24 at 8 p.m. EDT.